Dull sublunary lovers' love (Whose soul is sense) cannot admit
Alright, alright, just in case you haven't put two and two together, let's get this metaphor wrapped up and for all. Stanza 4 moves us away from the natural disasters and is going to connect it back with his argument.
Line 13 is a mini tongue-twister, with lots of playful L sounds twisting through it. The playfulness of his argument is also emphasized by the repetitive phrase, "lovers' love."
We also skip right into this line by losing the first syllable. We ought to start with an unstressed syllable here, but we hop right in with the thudding sound of "Dull." After that, things go right back to the iambic pattern we expect to see.
"Sublunary" is a fancy, Latinate way of saying "beneath the moon." More specifically, he is connecting shallow lovers' love to earthbound earthquakes, as opposed to the motions of heavenly bodies.
The parenthetical note really spells out what makes this type of love so wrong. With the alliteration of "Whose soul is sense," Donne explains that earthly lovers are only connected by earthly things, namely the five senses.
Line 14 ends with a cliffhanger. This is the first real enjambment of the poem, meaning a line break that also breaks up a continuing thought. Tune into the next line to find out what these lovers can't admit!
The enjambment also allows for the more common definition of "admit": confess, to assert itself.
Absence, because it doth remove Those things which elemented it.
The first word of line 15 is like a punchline. First, we were waiting for the resolution to the previous line. What can't they admit? Just tell us, already! Second, "absence" is another trochee, meaning a reversed iambic foot that puts the stressed syllable before the unstressed one. This adds to the emphasis that we naturally feel.
The rest of these two lines are unpacking the crafty logic of Donne: The reason that these shallow lovers can't stand to be apart from one another is that their entire relationship is based on their physical presence. They can't unglue themselves from one another for two seconds. Because their physical desires started ("elemented") their love, absence extinguishes it. In your face, shallow lovers.